Need a quick help from the DB experts: I have two tables: HOURS SSN Start End ID --- --- --- 3 --- --- --- 3 --- --- --- 5 --- --- --- 5 --- --- --- 5 --- --- --- 5 LOCATION Addr Num --- 1 --- 2 --- 3 --- 4 --- 5 On the first table, the value of SSN is redundant, so is the ID; therefore there's no particular Primary Key choice. However, a composite key can be used taking SSN and ID together, which makes the combined fields unique. Now, the Num and ID are related (i.e., HOURS.ID = Location.Num). The problem: Listing the ones that are absent in ID, but are present in Num, which means the output should be : 1 2 4 or anything representing them, such as the list of 'addr's corresponding to 1,2 and 4. I spent too much of time on this. Hope someone knows the way out.